The present invention pertains to advantageous new low temperature processes for synthesizing rare-earth oxysulfide light-emitting phosphors.
Oxysulfide phosphors, which are used in all of the display technologies, are desirable commercial products because of their high luminance efficiency. For example, red, green, and blue emitting phosphors (three different phosphors) are used in every television, computer monitor, and cathode ray tube produced. They are used in electron beams and X-ray digitized image displays. Phosphors are also used in the lighting industry, for example, in fluorescent light bulbs.
Current oxysulfide phosphor synthesis methods produce phosphors with sufficient luminosity, but these processes have significant disadvantages in terms of operating costs and processing time. For example, current methods require process temperatures in excess of 500° C. In one method, process temperatures as high as 1350° C. are reached in production of oxysulfide phosphors. Operating and equipment costs associated with reaching and maintaining temperatures of this magnitude create a need for lower temperature methods of preparation.
In addition, some methods require inert gases such as nitrogen for the reaction environment. The extra equipment for maintenance of the inert atmosphere in addition to the operating expense of buying a specialty gas creates a need for a process utilizing cheaper accessible reactants.
Also, reaction times are frequently an hour or more. Combined with the multiple steps required to prepare, react, and purify the oxysulfide phosphor, the total processing time is often hours. A shorter reaction and processing time is desirable because product may be made more frequently or on short demand time.
Therefore, it is desirable to find a method to produce rare-earth oxysulfide phosphors without the disadvantages of the known methods, thus reducing the operating costs. Because both the display and lighting markets, which deal with consumer items, are very cost competitive, any process that reduces cost will have a huge potential impact.